Osmosis + investigating the effects of osmosis on plant tissue required practical

Question 1

Define osmosis

Answer 1

Osmosis is the net movement of water molecules from an area of high water concentration (a dilute solution) to an area of lower water concentration (a concentrated solution) across a partially permeable membrane

Question 2

In terms of concentration of water, what does a dilute sugar solution contain

Answer 2

Dilute sugar solutions contain a high concentration of water (the solvent) and a low concentration of sugar (the solute)

Question 3

In terms of concentration of water, what does a concentrated sugar solution contain

Answer 3

Concentrated sugar solutions contain a low concentration of water (the solvent) and a high concentration of sugar (the solute)

Question 4

What is a partially permeable membrane

Answer 4

A partially permeable membrane is a membrane that allows only certain substances to pass through
e.g. the membrane allows water molecules to pass through but not sugar molecules

Question 5

State the difference between diffusion and active transport

Answer 5

In diffusion all particles move freely down concentration gradients.
In osmosis only water (solvent) molecules move across a partially
permeable membrane from a dilute solution to a concentrated solution.

Question 6

Describe what will happen in this image
https://bam.files.bbci.co.uk/bam/live/content/zpfb2nb/small

Answer 6

There is a higher concentration of water on the left hand side and a lower concentration of water on the right hand side.
Therefore the water now
diffuses from the left hand side to the right hand side.

Question 7

Describe the concentration of the cytoplasm

Answer 7

The cytoplasm of cells is a relatively concentrated solution. It contains a relatively low concentration of water.

Question 8

How can the cytoplasm become more concentrated

Answer 8

If a cell uses up water in its chemical reactions, the cytoplasm becomes more concentrated

Question 9

How can the cytoplasm become too dilute

Answer 9

The cytoplasm becomes too dilute when more water is made in chemical reactions

Question 10

What happens if we place an animal cell in water

Answer 10

If an animal cell is placed in water, then osmosis will take place. Water will move by osmosis from outside the cell to inside the cell (from an area of higher water concentration to an area of lower water concentration)
The water moving in will cause the cell expand. The cell could even burst

Question 11

What happens if we place an animal cell in a very concentrated solution

Answer 11

If we place an animal cell in a very concentrated solution, the water will move out of the cell by osmosis (the water will move from an area of higher water concentration to an area of lower water concentration). This will cause the cell to shrink, shrivel up and no longer survive.

Question 12

What happens if we place a plant cell in water

Answer 12

If we place a plant cell in water, then water will move by osmosis from outside the cell to inside the cell . This will cause the cell to expand. The cell wall prevents the plant cell from bursting. Instead the cell becomes swollen. The cell has become turgid

Question 13

What happens if we place the plant cell into a concentrated solution

Answer 13

If we place the plant cell into a concentrated solution, then water moves out of the cell by osmosis. This causes the cell to shrink. The cell has become flaccid

Question 14

What happens if we place the plant cell into a concentrated solution

Answer 14

If we place the plant cell into a concentrated solution, then water moves out of the cell by osmosis. This causes the cell to shrink. The cell has become flaccid.

Question 15

Describe how to investigate the effects of osmosis on plant tissue

Answer 15

Cut up a potato into identical cylinders of the same size

Measure the mass of each cylinder using a balance.

Place each cylinder into a test tube and add different concentrations of sugar solutions in each of the test tubes.
Ensure that one of the test tubes is filled with distilled water. (the reason that distilled water is used is because distilled water contains no dissolved substances and dissolved substances could affect teh rate of osmosis) r
Leave the potato cylinders overnight to allow osmosis to take place.
Next remove the potato cylinders and gently roll them on a paper towel to remove any surface moisture

Measure the mass of the cylinders again.

If the cylinders have drawn in water by osmosis, they would have increased in mass
If water has been drawn out they would have decreased in mass
Calculate the percentage change. By calculating percentage change you can compare the effect of the sugar solution on cylinders that didn’t have the same initial mass. An increase in mass will give a positive percentage change and a decrease in mass will give a negative percentage change

Question 16

How to calculate percentage change

Answer 16

percentage change = change in value/original value x 100

Question 17

A potato cylinder has a starting mass of 1.56g. This increases by 0.25g. Calculate the percentage increase

Answer 17

percentage change = change in value/original value x 100

% change = 0.25/1.56 x 100
% change = +16.03% to 2dp

Question 18

A potato cylinder has a starting mass of 1.32g.
This decreases by 0.19g
Calculate the percentage decrease

Answer 18

percentage change = change in value/original value x 100

% change = -0.19/1.32 x 100
% change = -14.39% to 2d.p.

Question 19

Describe the graph
https://cdn.savemyexams.co.uk/cdn-cgi/image/w=640,f=auto/uploads/2020/08/Osmosis-Analysis_2.png

supposed to be a curved line

Answer 19

This graph shows that in water, the potato cylinder gains mass as water moves into it by osmosis. (arrow at the top of the graph)

However, in a concentrated sugar solution, the cylinder loses mass as water moves out of the cell by osmosis. (arrow at the bottom of the graph - line at the end)

As the concentration increases, the percentage change in mass decreased

Question 20

https://cdn.savemyexams.co.uk/cdn-cgi/image/w=640,f=auto/uploads/2020/08/Osmosis-Analysis_2.png

what does the point at which the line of best fit crosses the x-axis show

Answer 20

The point at which the line of best fit crosses the x-axis is the concentration of sugar inside the potato as this is where there would be no change in mass of the potato.

Where the line crosses the x axis there is no change in mass. This is because the concentration outside the cell is the same as the concentration inside the cell, so no overall osmosis takes place.
The point at which the line crosses the x axis is the concentration inside the cell.

Question 21

What is the dependent variable in this experiment

Answer 21

The dependent variable is the variable that you measure

The dependent variable is the mass of the potato

Question 22

What is the independent variable in this experiment

Answer 22

The independent variable is the variable you change

The independent variable is the concentration of the sugar solution.

Question 23

What are the control variables in this experiment

Answer 23

The control variables are the volume of the solution, the temperature of the solution, the time, the type of sugar used)

Question 24

Tube A has distilled water
Tube B 1.0 conc.
Tube C 2 conc.
Tube D. 3 conc.

Which potato cylinder would you expect to be shortest after 24 hours.
Explain your answer

Answer 24

The potato cylinder in tube D, because this type contains the most concentrated sugar solution so this cylinder will have lost the most water by osmosis

Question 25

Define active transport

Answer 25

Active transport is the movement of substances from a more dilute solution to a more concentrated solution against a concentration gradient. This requires energy from respiration

Question 26

Explain the differences between diffusion and active transport

Answer 26

In diffusion, particles move down the concentration gradient however in active transport, particles are moved against the concentration gradient.

Diffusion does not require energy from respiration however active transport requires energy from respiration.

Question 27

What does active transport need to occur. Where does it get this thing

Answer 27

Active transport requires energy from respiration

Question 28

Explain how active transport occurs in the small intestine

Answer 28

When the concentration of sugars in the small intestine is lower than the concentration of sugars inside blood, the sugars cannot diffuse into the blood

Therefore, active transport is used so that the sugar molecules can be absorbed from the lower concentrations
in the gut into the bloodstream which has a higher sugar concentration. The blood then carries the sugars around the body. Sugar molecules are used for cell respiration.

Question 29

Explain why cells that carry out a lot of active transport also usually have many mitochondria

Answer 29

The cellular respiration in the mitochondria releases energy needed for active
transport.
Cells that carry out a lot of active transport often have many mitochondria to meet their energy requirements.

Question 30

Explain how active transport occurs in root hair cells

Answer 30

Plants need to move mineral ions from the soil into their roots.
Mineral ion solutions in the soil are much more dilute than the solution in
plant root hair cells,
so they are moved against a concentration gradient into the root hair cell using active transport

Question 31

What are sugar molecules used for in the body

Answer 31

Sugar molecules are used for respiration in the body.

Question 32

Explain how active transport differs from diffusion and osmosis

Answer 32

In active transport, substances moved against concentration gradient across partially
permeable membrane
process uses energy supplied by cellular respiration.
However in osmosis and diffusion
substances moved down concentration gradient (diffusion) or water
concentration (osmosis) alsobn no requirement for energy from respiration